(Soft) deletion of courses

[krishnans2006]

Currently, courses cannot be deleted. This is because doing so would delete many assignments, submissions, quiz logs, etc. which are vital to keep for administrative purposes. Removing the on_delete=CASCADE for these relations is not a reasonable solution.

So, it would be nice to implement a "soft deletion" feature for courses. Teachers can be given an option to let students:

• Access assignments/submissions and submit code (read-write)
• Access assignments/submissions but not submit code (read-only)
• Access nothing (the course appears deleted)

In all of these scenarios, the course should not show up on the home page as a normal course; instead, it could be put in a collapsed section for hidden courses (for both students and teachers). Teachers of the course (and administrators) should always be able to access and edit the course as needed.

Currently, some courses on Tin implement this functionality by removing all students from the course at the end of the year. This makes it difficult to easily access student code in the future, which is the main inspiration for this feature.